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How the chest works
The main chest muscle is the pectoralis major. It has an upper (clavicular) portion that attaches to the collarbone and a larger lower (sternocostal) portion that attaches to the breastbone and ribs. Together they bring the upper arm across the body, press it forward and rotate it inward. The smaller pectoralis minor sits underneath and helps move the shoulder blade. Presses also work the front of the shoulders and the triceps.
